Thermostatic snap switches of the temperature actuated type are used in electric frypans and similar devices and usually comprise a housing having a projecting probe as well as contact members so that the unit can be plugged into a frypan or the like and will then control the temperature by switch actuation.
Devices of this general type have a disadvantage in that they tend to cause electrical noises in equipment such as radios or television, this being due to the relatively slow movement of a thermostatic control member such as a bimetallic strip and causing some amount of arcing during the action of switching, and also the switching will cause pitting and damage to the contacts when directly achieved by the bimetallic strip.
For this purpose it has been proposed in an earlier invention of ours, the subject of Australian patent application No. 84063/75, (PB8571/74) dated Aug. 19, 1974 to use a magnetic switching device under influence of the thermostatic switching member to achieve an overbalance when a particular condition exits to give rapid opening or closing of the contacts of the switch.
Such a device has been found to be particularly effective in that it is sensitive to pressure by the bimetallic strip to load the switching member to a point where a snap action is achieved due to the influence of the magnetic holding device.
The present invention again uses a snap action device as its switch, but instead of using a magnetic control member, control in this case is by a tensioned switch blade which overbalances to either the open or the closed position of the contacts when appropriate pressure is applied to a support blade which carries the switch blade.
The invention comprises a temperature sensitive member mounted to contact and deflect a support blade for a snap action over balancing switch blade which carries a movable contact in engageable relationship with a fixed contact, the overbalancing point of the switch blade being adjustable by engaging a tensioning member on the switch blade on a tongue which is adjustable in position within and/or through the plane of movement of the switch blade.
In order however to enable the invention to be fully appreciated an embodiment will now be described with reference to the accompanying drawings, but it is to be clear that the invention is not to be limited to the details disclosed hereinafter, the scope being defined in the claims.